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From: freeman@spar.SPAR.SLB.COM (Jay Freeman)
Newsgroups: sci.space,sci.space.shuttle
Subject: Re: In-flight obsolescence
Message-ID: <62@spar.SPAR.SLB.COM>
Date: Tue, 18-Nov-86 15:54:01 EST
Article-I.D.: spar.62
Posted: Tue Nov 18 15:54:01 1986
Date-Received: Wed, 19-Nov-86 05:39:29 EST
References: <7325@utzoo.UUCP> <260@pixar.UUCP>
Reply-To: freeman@spar.UUCP (Jay Freeman)
Organization: Schlumberger Palo Alto Research - CASLAB
Lines: 41
Xref: mnetor sci.space:163 sci.space.shuttle:35

In article <260@pixar.UUCP> good@pixar.UUCP (Void where prohibited) writes:
>In article <7325@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>>JPL is studying a mission dubbed TAU, Thousand Astronomical Units...
>>...propulsion system would be shed after fuel exhaustion, leaving the
>>11,000-lb spacecraft to continue on for up to 40 more years...
>>
>>[Mini-editorial:  a probe with a 50-year mission will be passed by newer
>>probes with better engines long before the end of its mission.  Planning
>>for such long missions needs to consider in-flight obsolescence.  -- HS]
>
>Good point.  But better engines will result, at least in part, from experience
>gained by flying the current idea of "new" engines.  I also wonder if the
>probe might not return some data significant for the planning of a follow-up
>mission during the first few years.
>
>
>
>-- 
>		--Craig
>		...{ucbvax,sun}!pixar!good


Furthermore, there is reasonably good science to be done at order of 100
AU -- nominal distance for the (presumed) shock front at which the
solar wind slows down abruptly due to interaction with the interstellar
medium.  A mission would presumably study this region, as well as study
the nature of the unperturbed interstellar medium not far beyond.  It is
probably worth developing an advanced engine just to get to there, and
if it doesn't cost too much more to make the vehicle last longer, so
much the better.

Besides, direct measurement of stellar distances benefits in proportion
to the distance traveled.  At 100 AU one would be only 10% as well
off as at 1000 AU, but 50 times better off than here (our baseline
is 2 AU, the diameter of the Earth's orbit).

One might indeed need some of those interim measurements as an aid to
mission planning for the interstellar missions to be launched with
the advanced engines developed during the next 40 years ...

					-- Jay Freeman